1. Field of the Invention
The present invention relates to a tape withdrawal and tensioning mechanism for a video cassette recorder/reproducer and, more particularly, to a mechanism for accurately and reliably withdrawing tape from a video cassette to prepare the tape for threading around a video scanner and for controlling the tension in the tape.
2. Description of the Prior Art
Video recording tape is commonly supplied in a standard type of cassette to eliminate the problems associated with open reels and the threading of the tape into a video recorder/reproducer. When using a standard video cassette with a video recorder/reproducer, the cassette must be loaded into the system and the reels within the cassette must be mated to the reel drive system of the recorder/reproducer. Thereafter, the tape must be withdrawn from the cassette so that it may be threaded around the video scanner of the recorder/reproducer.
The video recorder/reproducers and associated mechanisms that have been developed heretofore have been intended for use in the recording and playing back of standard television type signals in either a home or commercial environment. In such systems, each tape is not used extensively and the information recorded thereon is relatively unimportant so that the careful handling of the tape to maximize the life thereof and to preserve the information thereon has not been an important requirement. For similar reasons, accuracy and reliability of operation have been relatively unimportant considerations. It has also been relatively unimportant that a tape recorded on one machine be playable on another machine and vice versa since usually a single machine was used for recording and playing back information.
Furthermore, in prior systems, the tape travels at low speeds, typically 33/4 inches per second during playback and 45 inches per second during rewind. As a result, controlling the tension in the tape has also been relatively unimportant and an open loop system has generally been used. In other words, a friction break system has been applied to the supply reel to keep the tension within a given range and a friction clutch drive system has normally been utilized for the take-up reel to apply a constant torque thereto and to control the tension in the tape.
On the other hand, the present mechanism is designed for a video recorder/reproducer intended for use in a document acquisition and retrieval system. This environment places a number of constraints on the video tape and the manner in which it is handled which cannot be satisfied with conventional tape handling mechanisms. For example, in such an environment, significant quantities of data, including address information, may be loaded on a sigle tape, representing a substantial investment in programming and information. Furthermore, the tape may be loaded and unloaded into the system many times each day. Therefore, in order to preserve the data and to maximize the life of the tape, it becomes critical that the tape be protected and handled in a very gentle manner. Since a tape will typically be recorded in one machine and played back in another machine, it is important that the mechanism that handles that tape does so accurately and reliably so that the tape does not sense any differences from one machine to another.
Still further, in a document acquisition and retrieval system, the tape travels in two directions, during a search mode, at speeds in excess of 400 inches per second and the tape accelerates to such speeds in approximately one second. In handling tape under such conditions, constant torque drive systems and friction breaks simply cannot provide the tape constraints necessary to make a workable system. Servo motors and closed loop servo systems must be used and the tension in the tape must be accurately controlled in order to insure proper tracking and winding of the tape. A video cassette recorder/reproducer incorporating a mechanism which handles tape in a manner which meets the above requirements has been unavailable heretofore.